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Variable Scopes and Shadowing

Understand variable scopes and shadowing in Go, along with an overview of zero values.

We'll cover the following...

A scope is part of the program in which a variable can be seen. In Go, we have the following variable scopes:

  • Package scoped: Can be seen by the entire package and is declared outside a function

  • Function scoped: Can be seen within {} which defines the function

  • Statement scoped: Can be seen within {} of a statement in a function (for loop, if/else)

In the following program, the word variable is declared at the package level. It can be used by any function defined in the package:

Go (1.18.2)
package main
import "fmt"
var word = "hello"
func main() {
    fmt.Println(word)
}

In the following program, the word variable is defined inside the main() function and can only be used inside {} which defines main. Outside, it is undefined:

Go (1.18.2)
package main
import "fmt"
func main() {
    var word string = "hello"
    fmt.Println(word)
}

Finally, in this program, i is statement scoped. It can be used on the line ...